In certain states of disease affecting the human backbone, for instance intervertebral disc displacement, conditions of pain provoked by the disc, so-called whiplash injuries and also other problems and injuries relating to the back such as fractures in the bodies of vertebrae, or other pathological changes in the body of vertebra or other parts of the disc, there is a need for instruments and methods of measurement for detection and analysis of the condition, in the core of each intervertebral disc respectively, which below is called disc, and in the vertebrae themselves.
Since measurement in the disc clarifies the strain on the back, there is also a need for an instrument for determination of the strain the back is subject to, e.g. during work, in specific body positions, at the carrying out of surgical operations, e.g. stabilization and/or correction operations, and for specific external strains on the vertebral column. Such a determination might be needed for medical and ergonomical reasons, but also to find a shape or design that is optimal for the strain on the back for e.g. a chair, a tool or a mattress/bed to provide a functionality and/or comfort.
Knowledge of the pressure in a disc or a body of vertebra before or after injection of fluid or pharmaceuticals can facilitate or be an indication of the reached result even in cases of e.g. so-called vertebroplastics or kyfoplastics, i.e. operations in such a form that bone cement or similar is being injected into fractured discs, preferably in elderly, to accomplish reposition, stability in the fracture and pain release.
Knowledge of the pressure conditions also in the adjacent discs or in the injured body of vertebra can increase safety in connection with these operations and also increase the possibilities to adequately fix or to reduce a fracture. The possibility, for certain pathological changes in the discs, e.g. tumours, to inject the pharmaceutical locally into the tumour also calls for knowledge of the present pressure in the changed area.
The nucleus, called nucleus pulposus, in each disc respectively, constitutes a central part of the disc and comprises a semi-liquid, gelatinous substance. The nucleus is surrounded by a peripheric portion, called anulus fibrosus, consisting of fibro cartilage. Higher up in age there is a hydrostatic pressure in nucleus pulposus. A change in pressure in the nucleus arises with altered strain on the back and with different movements. With increasing age the pressure in nucleus changes, among others due to changed properties in the nucleus and the surrounding anulus fibrosus.
A known method for investigating the nucleus in a disc is discography. Discography is thus used to evaluate if there are changes in the disc affecting the mechanical properties of the disc, but above all to establish whether the disc is a cause for back pain.
At discography a fluid is injected under pressure into the disc using for instance a syringe. The injection of fluid into a pathologically changed disc will lead to a sensation of pain for the patient. If the sensation of pain is the same or very similar to that for which the patient seeks help, the provocation of pain is interpreted as an indication that the pain, and hence the discomfort of the patient, is being generated from the examined disc. The reaction of pain is accomplished as the injected liquid generates an increased pressure in the nucleus of the disc and causes a tension or strain in an already inflamed disc tissue, or as the increased pressure causes ruptures in changed disc tissue that is a result of illness or age.
With the patent document U.S. Pat. No. 6,370,420, a system for discography is previously known wherein injection of contrast fluids and subsequent measurement is preformed of the pressure in the contrast medium that has been added to each disc, respectively, using a pressure sensor arranged outside the disc. When the pressure in the contrast medium increases in the disc, information from the measured pressure in the contrast medium, photos of the patients facial expression at the time of injection, sound recordings of the patients voice of expression, x-ray images of the disc during the injection of contrast liquid, is compiled. This compiled information then forms the basis of a subjective assessment of the patient's pain level in the disc in question and is thus no exact measuring method.
Further, through the document WO 2007/0112299 a device for injection of a liquid into a disc at discography is previously known. The device comprises pressure and volume sensors, arranged outside of the disc, for sensoring of pressure and volume in the liquid that is fed to each disc, respectively. This device measures the pressure and volume of the added liquid outside of the disc in the system, and not the actual pressure inside the disc. Even with this device a subjective assessment of the patient's pain level in the disc in question is achieved and is thus not an exact measuring method.